Porous sound absorbing structure

ABSTRACT

A porous sound absorbing structure according to the present invention includes an outer material  2  having a smooth curved shape, an inner material  3  having an uneven shape with a perimeter thereof combined with a perimeter of the outer material  2  to form a hollow portion S between the outer material  2  and the inner material, and a reinforcing plate material  4  having a large number of through holes  5,  the reinforcing plate material being attached to a surface of the inner material  3  on the side of the hollow portion S in such a manner that an air layer is formed between the reinforcing plate material and the surface. A sound absorbing property is given to an interior of the hollow portion S by the reinforcing plate material  4.

TECHNICAL FIELD

The present invention relates to a porous sound absorbing structurehaving a sound absorbing property. Further, the present inventionrelates to a porous sound absorbing structure to be favorably applied toparts forming an automobile.

BACKGROUND ART

This type of technique is described in Patent Document 1 for example. Ina sound absorbing structure described in Patent Document 1, a fibermaterial and a porous plate are provided so as to overlie each other,and an air layer is provided behind the porous plate or the fibermaterial. Density ρ (kg/m³) of the fiber material and thickness t (mm)of the fiber material preferably satisfy the relationship of p×t≧0.01kg/m².

CITATION LIST Patent Document

[Patent Document 1] JP 2006-199276 A

SUMMARY OF INVENTION Problems to be Solved by Invention

In a case where the sound absorbing structure described in PatentDocument 1 is applied to a hood (also called as a bonnet) of anautomobile for example, the fiber material (fiber sound absorbingmaterial) is attached to a lower surface (on the side of an engine) ofan inner material (porous plate) of the hood (refer to FIG. 1 of PatentDocument 1).

Meanwhile, from a viewpoint to protect pedestrians (to absorb shock), alarge distance between the inner material and the engine is led toimprovement of a shock absorbing property. Therefore, reduction of aspace in an engine room by attaching the fiber sound absorbing materialto the lower surface of the inner material is desirably avoided as faras possible.

A sound absorption coefficient of the inner material (porous plate) ismaximized with a particular frequency which is determined by a holediameter thereof, a hole pitch, and a distance between the innermaterial and an outer material (thickness of the air layer). When thedistance between the inner material and the outer material is relativelylarge, a high-frequency sound is not easily absorbed only by the innermaterial (porous plate). This is because with thickness of the air layerbeing increased, the inner material (porous plate) comes to absorb alow-frequency sound. It should be noted that normally, the distancebetween the inner material and the outer material cannot be determinedwhile assigning a priority to giving the sound absorbing property.

Therefore, in the sound absorbing structure described in Patent Document1, by the fiber material (fiber sound absorbing material), ahigh-frequency sound such as 1 kHz or higher is absorbed. Thus, when thefiber sound absorbing material is simply taken off from the lowersurface of the inner material in order not to reduce the space in theengine room, there is a concern that the sound absorbing property forthe high-frequency sound is lowered.

The present invention is achieved in consideration with the situationdescribed above, and an object thereof is to provide a porous soundabsorbing structure capable of easily increasing a frequency range withwhich a sound absorption coefficient is great without attaching a fibersound absorbing material to a lower surface of an inner material (insidematerial).

Means for Solving Problems

The present invention is a porous sound absorbing structure including anoutside material having a smooth curved shape, an inside material havingan uneven shape with a perimeter thereof combined with a perimeter ofthe outside material to form a hollow portion between the outsidematerial and the inside material, and a reinforcing plate materialhaving a large number of through holes, the reinforcing plate materialbeing attached to a surface of at least any of the outside material andthe inside material on the side of the hollow portion in such a mannerthat an air layer is formed between the reinforcing plate material andthe surface. In this porous sound absorbing structure, a sound absorbingproperty is given to an interior of the hollow portion by thereinforcing plate material.

Effects of Invention

The reinforcing plate material is positioned between the outsidematerial (outer material) and the inside material (inner material).Therefore, thickness of the behind air layer of the reinforcing platematerial is smaller than for example the thickness of the behind airlayer of the porous plate (inner material) described in Patent Document1 under the same conditions. When the thickness of the behind air layeris decreased, the reinforcing plate material having a large number ofthrough holes absorbs a higher-frequency sound for a decreased amount ofthe thickness of the behind air layer.

The original function (role) of the reinforcing plate material is toreinforce the outside material and/or the inside material. By utilizingthe reinforcing plate material, without adding a new member for giving asound absorbing property to an object item, that is, easily, the soundabsorbing property can be given to the object item.

In such a way, according to the present invention, a frequency rangewith which a sound absorption coefficient is great can be easilyincreased without attaching a fiber sound absorbing material to a lowersurface of the inner material (inside material).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a view in which a first embodiment of a hood of anautomobile to which a porous sound absorbing structure of the presentinvention is applied is seen from the back; and FIG. 1(b) is a sectionalview taken along the line A-A of FIG. 1(a).

FIG. 2(a) is a view in which a second embodiment of a hood of theautomobile to which the porous sound absorbing structure of the presentinvention is applied is seen from the back; and FIG. 2(b) is a sectionalview taken along the line B-B of FIG. 2(a).

FIG. 3(a) is a view in which a third embodiment of a hood of theautomobile to which the porous sound absorbing structure of the presentinvention is applied is seen from the back; and FIG. 3(b) is a sectionalview taken along the line C-C of FIG. 3(a).

FIG. 4(a) is a view in which a fourth embodiment of a hood of theautomobile to which the porous sound absorbing structure of the presentinvention is applied is seen from the back; and FIG. 4(b) is a sectionalview taken along the line D-D of FIG. 4(a).

FIG. 5 is a view showing one embodiment of a door of the automobile towhich the porous sound absorbing structure of the present invention isapplied.

FIG. 6 is a graph showing a sound isolation property of the hood shownin FIGS. 1(a) and 1(b).

FIG. 7 is a graph showing a sound absorbing property of the hood shownin FIGS. 2(a) and 2(b).

FIG. 8 is a graph showing a sound absorbing property of the hood shownin FIGS. 3(a) and 3(b).

FIG. 9 is a perspective view showing a side body of the automobile.

FIGS. 10(a), 10(b), 10(c), and 10(d) are a sectional view taken alongthe line A-A of the side body shown in FIG. 9, a sectional view takenalong the line B-B, a sectional view taken along the line C-C, and asectional view taken along the line D-D, respectively.

MODES FOR CARRYING OUT INVENTION

Hereinafter, modes for carrying out the present invention will bedescribed with reference to the drawings. Examples of a case where aporous sound absorbing structure of the present invention is applied toparts forming an automobile will be shown below. It should be noted thatan object to which the present invention is applied is not limited tothe parts forming the automobile.

Hood (First Embodiment)

FIGS. 1 to 4 are views showing examples of a case where the porous soundabsorbing structure of the present invention is applied to a hood (alsocalled as a bonnet) of the automobile. FIG. 1 among FIGS. 1 to 4 shows ahood 1 (porous sound absorbing structural body) of a first embodiment.FIG. 1(a) is a view in which the hood 1 is seen from the back, and FIG.1(b) is a sectional view taken along the line A-A of FIG. 1(a).

As shown in FIGS. 1(a) and 1(b), the hood 1 is formed by bonding anouter material 2 (outside material) having a smooth curved shape and aninner material 3 (inside material) having an uneven shape at perimeterportions thereof by means of welding or the like.

A reinforcing plate material 4 is housed in a hollow portion S formedbetween the outer material 2 and the inner material 3. The reinforcingplate material 4 is fixed to a surface of the outer material 2 on theside of the hollow portion S at a perimeter portion (edge portion)thereof.

The outer material 2 of the hood 1 is a thin plate in order to easeshock at the time of collision against pedestrians from a viewpoint toprotect pedestrians or from a viewpoint to reduce weight and cost andthe like. Therefore, the reinforcing plate material 4 is attached to aback surface of the outer material 2 so that the outer material 2 is noteasily dented when being pressed by a person.

Materials of the outer material 2, the inner material 3, and thereinforcing plate material 4 are aluminum or an aluminum alloy. Itshould be noted that metal materials such as iron may be used as thematerials of the outer material 2, the inner material 3, and thereinforcing plate material 4.

As shown in FIG. 1(a), in the present example, the reinforcing platematerial 4 is formed in a substantially oblong shape. As shown in FIG.1(b), a sectional shape of the reinforcing plate material 4 has twomountain portions 4 a, 4 b, and a part between the mountain portions 4a, 4 b serves as a valley portion 4 c having predetermined width. An airlayer (behind air layer) is formed between the mountain portions 4 a, 4b and the valley portion 4 c, and the outer material 2. It should benoted that the shape of the reinforcing plate material 4 shown in FIG.1(a) is one example. That is, the reinforcing plate material in thepresent invention is not limited to the one having the shape of thepresent embodiment.

The reinforcing plate material 4 may also be fixed to a surface of notthe outer material 2 but the inner material 3 on the side of the hollowportion S in a mode where an air layer is formed between the reinforcingplate material and the surface. Further, reinforcing plate materials maybe respectively fixed to the surfaces of the outer material 2 and theinner material 3 respectively on the side of the hollow portion S in amode where air layers are formed between the reinforcing plate materialsand the surfaces.

In the present invention, by providing a large number of holes 5(through holes) in this reinforcing plate material 4, a sound absorbingproperty is given to an interior of the hollow portion S. A soundabsorption coefficient of the reinforcing plate material 4 is maximizedwith a particular frequency which is determined by a diameter of theholes 5, a pitch of the holes 5, and a distance between the reinforcingplate material 4 and the outer material 2 (thickness of the behind airlayer). It should be noted that thickness of the behind air layer can bechanged by the sectional shape of the reinforcing plate material 4.

From a viewpoint of mass-productivity, a diameter d₁ (mm) of the holes 5is preferably 0.7 t₁≦d₁≦1.3 t₁. It should be noted that t₁ (mm) denotesplate thickness of the reinforcing plate material 4. The plate thicknesst₁ (mm) of the reinforcing plate material 4 is approximately 0.8≦t₁≦1.2.It should be noted that plate thickness of the outer material 2 and theinner material 3 is also approximately 0.8 mm or more and 1.2 mm orless. The holes 5 are provided so that strength of the reinforcing platematerial 4 does not become less than the strength that the reinforcingplate material should have. That is, the number and the pitch of theholes 5 are determined in consideration with the strength of thereinforcing plate material 4.

Hood (Second Embodiment)

FIG. 2 shows a hood 102 of a second embodiment. FIG. 2(a) is a view inwhich the hood 102 is seen from the back, and FIG. 2(b) is a sectionalview taken along the line B-B of FIG. 2(a). In FIGS. 2(a) and 2(b),similar members to those of the hood 1 of the first embodiment will begiven the same reference numerals (the same is applied to the otherembodiments).

A difference between the hood 102 and the hood 1 shown in FIGS. 1(a) and1(b) is a point that opening portions 3 a are provided in the innermaterial 3 in the hood 102.

On the back surface side of the hood 102, that is, on the right side ofthe hood 102 in FIG. 2(b), an engine is positioned in a state where thehood 102 is closed. The opening portions 3 a are to guide a sound (soundwaves) produced by the engine to the reinforcing plate material 4 placedin the hollow portion S and provided with a large number of holes 5. Inthe present embodiment, the opening portions 3 a are provided atpositions to face the reinforcing plate material 4 so that the sound(sound waves) is easily guided to the reinforcing plate material 4. Theplurality of opening portions 3 a is arranged in a zigzag manner. Itshould be noted that although the plurality of opening portions 3 a isprovided in the inner material 3 in this example, the number of theopening portions 3 a may be one. A shape of the opening portions 3 a isnot limited to an oblong shape.

Hood (Third Embodiment)

FIG. 3 shows a hood 103 of a third embodiment. FIG. 3(a) is a view inwhich the hood 103 is seen from the back, and FIG. 3(b) is a sectionalview taken along the line C-C of FIG. 3(a).

A difference between the hood 103 and the hood 102 shown in FIGS. 2(a)and 2(b) is a point that in the hood 103, not only the reinforcing platematerial 4 but also the inner material 3 is provided with a large numberof holes 6 (through holes), so that the sound absorbing property isgiven to the inner material 3 itself.

The reinforcing plate material 4 provided with a large number of holes 5is arranged in a front part of the hood 103 in a plan view of the hood103. The opening portions 3 a are also provided on the front part sideof the hood 103 (inner material 3) in accordance with the reinforcingplate material 4. Meanwhile, a position of a sound absorbing portion 12(region where the holes 6 are provided) formed in the inner material 3itself is set on the rear side of the reinforcing plate material 4 andthe opening portions 3 a. That is, the position of the sound absorbingportion 12 is set on the rear side of the center of the hood 103 (innermaterial 3). In such a mode, when seen from the engine (sound source),the reinforcing plate material 4 and the sound absorbing portion 12 aredisplaced from each other so as to be set at positions not overlyingeach other.

Since the reinforcing plate material 4 and the sound absorbing portion12 are displaced from each other when seen from the engine (soundsource), an air layer on the back side of the porous plate portions (thereinforcing plate material 4 and the sound absorbing portion 12) becomesa behind air layer more suitable for sound absorption. Regarding thesound absorbing portion 12, this is because an opposing surface on theback side of the porous plate portion can be surely closed. The soundfrom the engine (sound source) is easily introduced to the respectiveporous plate portions (the reinforcing plate material 4 and the soundabsorbing portion 12). Thereby, the sound absorbing property is moreimproved.

It should be noted that the positions of the opening portions 3 afurther preferably come closer to a front side end (one end) of the hood103 (inner material 3) than the positions shown in FIG. 3. Thereby, adistance between the opening portions 3 a and the sound absorbingportion 12 is increased. When the distance between the opening portions3 a and the sound absorbing portion 12 is large, an influence of theopening portions 3 a on a sound absorbing performance of the soundabsorbing portion 12 is reduced. When the distance between the soundabsorbing portion 12 and the opening portions 3 a is decreased, thebehind air of the sound absorbing portion 12 easily comes in to and outfrom the opening portions 3 a. Thus, a valid behind air layer isextended, so that the designed sound absorbing performance of the soundabsorbing portion 12 cannot be exhibited. Meanwhile, by increasing thedistance between the sound absorbing portion 12 and the opening portions3 a, an influence of the opening portions 3 a on the behind air layer ofthe sound absorbing portion 12 is reduced. As a result, the designedsound absorbing performance of the sound absorbing portion 12 can beefficiently exhibited. Thereby, the sound absorbing property is furtherimproved for the whole hood 103. In such a way, the opening portions 3 aand the sound absorbing portion 12 are preferably estranged from eachother by as a long distance as possible.

From a viewpoint of mass-productivity, a diameter d₂ (mm) of the holes 6is preferably 0.7 t₂≦d₂≦1.3 t₂. It should be noted that t₂ (mm) denotesplate thickness of the inner material 3. The same relationship betweenthe hole diameter and the plate thickness is applied to a case whereholes for giving the sound absorbing property are provided in the outermaterial 2.

Hood (Fourth Embodiment)

FIG. 4 shows a hood 104 of a fourth embodiment. FIG. 4(a) is a view inwhich the hood 104 is seen from the back, and FIG. 4(b) is a sectionalview taken along the line D-D of FIG. 4(a).

A difference between the hood 104 and the hood 103 shown in FIGS. 3(a)and 3(b) is a point that the inner material 3 of the hood 104 is notprovided with the opening portions 3 a for guiding the sound (soundwaves) to the reinforcing plate material 4. The other structures of thehood 104 are the same as those of the hood 103.

(Door)

FIG. 5 is a view showing one example of a case where the porous soundabsorbing structure of the present invention is applied to a door of theautomobile. It should be noted that FIG. 5 is a sectional view of thedoor of the automobile.

As shown in FIG. 5, a door 51 is formed by bonding an outer material 7(outside material) having a smooth curved shape and an inner material 8(inside material) having an uneven shape at perimeter portions thereofby means of welding or the like. A window glass 9 is housed in a hollowportion S formed between the outer material 7 and the inner material 8.

A reinforcing plate material 10 having a large number of holes 10 a(through holes) is fixed to a surface of the outer material 7 on theside of the hollow portion S in a mode where an air layer (behind airlayer) is formed between the reinforcing plate material and the surface.

A reinforcing plate material 11 having a large number of holes 11 a(through holes) is fixed to a surface of the inner material 8 on theside of the hollow portion S in a mode where an air layer (behind airlayer) is formed between the reinforcing plate material and the surface.

A sound absorption coefficient of the reinforcing plate material 10 (11)is maximized with a particular frequency which is determined by adiameter of the holes 10 a (11 a), a pitch of the holes 10 a (11 a), anda distance between the reinforcing plate material 10 (11) and the outermaterial 7 (inner material 8) (thickness of the behind air layer). Itshould be noted that thickness of the behind air layer can be changed bya sectional shape of the reinforcing plate material 10 (11).

Materials of the outer material 7, the inner material 8, and thereinforcing plate material 10, and the reinforcing plate material 11 arealuminum or an aluminum alloy as well as the hood. It should be notedthat other metal such as iron may also be used.

The reinforcing plate materials 10, 11 absorb a sound emitted from avehicle interior to a vehicle exterior such as a sound from anin-vehicle audio, and a sound coming from the vehicle exterior to thevehicle interior such as road noises and wind noises.

(Analysis Result of Emitted Sound Reduction Effect)

FIG. 6 is a graph showing a sound isolation property of the hood 1 shownin FIGS. 1(a) and 1(b). As seen from FIG. 6, by attaching thereinforcing plate material 4 provided with a large number of holes 5 tothe surface of the outer material 2 on the side of the hollow portion S,the sound absorbing structure with the behind air layer of the decreasedthickness can be formed more easily than the conventional example, sothat a frequency range with which the sound absorption coefficient isgreat can be easily increased. Thereby, a sound emitted from an engineroom to the vehicle exterior via the hood can be reduced.

FIG. 7 is a graph showing the sound absorbing property of the hood 102shown in FIGS. 2(a) and 2(b). In a design of the sound absorptioncoefficient of the hood 102, the behind air layer, the hole diameter, anaperture ratio of the holes, and the like of the reinforcing platematerial 4 are adjusted, so that the sound absorption coefficient of thesound of 1 kHz to 2 kHz is increased. As seen from FIG. 7, by providingthe opening portions 3 a for guiding the sound (sound waves) to thereinforcing plate material 4 to the surface of the inner material 3 towhich the reinforcing plate material 4 faces, a sound absorbing effectby the reinforcing plate material 4 is more exhibited.

FIG. 8 is a graph showing the sound absorbing property of the hood 103shown in FIGS. 3(a) and 3(b). In a design of the sound absorptioncoefficient of the hood 103, the behind air layer, the hole diameter, anaperture ratio of the holes, and the like of the reinforcing platematerial 4 are adjusted, so that the sound absorption coefficient of thesound of 1 kHz to 2 kHz is increased by the reinforcing plate material4. The hole diameter, an aperture ratio of the holes, and the like ofthe sound absorbing portion 12 of the inner material 3 are adjusted, sothat the sound absorption coefficient of the sound of 1.25 kHz to 3.15kHz is increased by the sound absorbing portion 12. As seen from FIG. 8,by providing the porous sound absorbing portion 12 in the inner material3 itself in addition to provision of the opening portions 3 a in thepart of the inner material 3 to which the reinforcing plate material 4faces, a sound absorbing effect by the inner material 3 itself can alsobe obtained in addition to the sound absorbing effect by the reinforcingplate material 4. Thereby, the sound absorbing performance can beimproved in a wider frequency range.

(Application to Parts forming Automobile other than Hood and Door)

FIG. 9 is a perspective view showing a side body 100 of the automobile.FIGS. 10(a), 10(b), 10(c), and 10(d) are a sectional view taken alongthe line A-A of the side body 100 shown in FIG. 9, a sectional viewtaken along the line B-B, a sectional view taken along the line C-C, anda sectional view taken along the line D-D, respectively.

FIG. 10(a) is a sectional view of a front pillar 41 of the side body100. The front pillar 41 is formed by bonding an outer material 21(outside material) having a smooth curved shape and an inner material 22(inside material) having an uneven shape at perimeter portions thereofby means of welding or the like. A reinforcing plate material 23 havinga large number of holes 23 a (through holes) is fixed to a surface ofthe outer material 21 on the side of a hollow portion in a mode where anair layer (behind air layer) is formed between the reinforcing platematerial and the surface. By this reinforcing plate material 23, thesound absorbing property is given to an interior of the hollow portionbetween the outer material 21 and the inner material 22.

FIG. 10(b) is a sectional view of a center pillar 42 of the side body100. As well as the front pillar 41 described above, the center pillar42 is provided with an outer material 24, an inner material 25, and areinforcing plate material 26 having a large number of through holes. Bythe reinforcing plate material 26, the sound absorbing property is givento an interior of a hollow portion between the outer material 24 and theinner material 25.

FIG. 10(c) is a sectional view of a rear pillar 43 of the side body 100.Regarding the rear pillar 43 as well, the rear pillar 43 is providedwith an outer material 27, an inner material 28, and a reinforcing platematerial 29 having a large number of through holes. By the reinforcingplate material 29, the sound absorbing property is given to an interiorof a hollow portion between the outer material 27 and the inner material28.

FIG. 10(d) is a sectional view of a side sill 44 of the side body 100.Regarding the side sill 44 as well, the side sill 44 is provided with anouter material 30, an inner material 31, and a reinforcing platematerial 32 having a large number of through holes. By the reinforcingplate material 32, the sound absorbing property is given to an interiorof a hollow portion between the outer material 30 and the inner material31.

In such a way, the porous sound absorbing structure of the presentinvention can be applied to various parts forming the automobile. Byapplying the porous sound absorbing structure of the present invention,engine noises, road noises, wind noises, vehicle-interior resonance, andthe like can be reduced.

A space in a vehicle-interior is desirably as large as possible. Thus,addition of a new part around the vehicle-interior is hard in terms ofspace. Therefore, a new part such as a sound absorbing material is noteasily added. Meanwhile, in the present invention, the sound absorbingproperty is developed by providing the holes in the part originallyrequired as a reinforcing member from a viewpoint to ensure strength.That is, according to the present invention, a sound insulationperformance can be improved without adding a new part.

(Operations and Effects)

As described above with many examples, with the porous sound absorbingstructure of the present invention, the reinforcing plate material ispositioned between the outside material (outer material) and the insidematerial (inner material). Therefore, the thickness of the behind airlayer of the reinforcing plate material is smaller than for example thethickness of the behind air layer of the porous inner material describedin Patent Document 1 under the same conditions. When the thickness ofthe behind air layer is decreased, the reinforcing plate material havinga large number of through holes absorbs a higher-frequency sound for adecreased amount of the thickness of the behind air layer.

The original function (role) of the reinforcing plate material is toreinforce the outside material and/or the inside material. By utilizingthe reinforcing plate material, without adding a new member for givingthe sound absorbing property to an object item, that is, easily, thesound absorbing property can be given to the object item. In such a way,according to the present invention, the frequency range with which thesound absorption coefficient is great can be easily increased withoutattaching a fiber sound absorbing material to a lower surface of theinner material (inside material).

In the present invention, an opening portion for guiding sound waves tothe reinforcing plate material in the hollow portion between the outsidematerial and the inside material is preferably provided in the outsidematerial and/or the inside material. With this configuration, the soundwaves are easily introduced to the reinforcing plate material, so thatthe sound absorbing effect by the reinforcing plate material isenhanced.

When the opening portion is provided at a position to face thereinforcing plate material, the sound waves are more easily introducedto the reinforcing plate material. Thus, the sound absorbing effect bythe reinforcing plate material is further enhanced.

Further, when, by also providing a large number of through holes notonly in the reinforcing plate material but also in the outside materialand/or the inside material, the sound absorbing property is given to theoutside material and/or the inside material itself, a sound absorbingeffect in a different frequency band from the reinforcing plate materialby the outside material and/or the inside material itself can beobtained in addition to the sound absorbing effect by the reinforcingplate material. Thereby, the sound absorbing performance can be improvedin a wider frequency range.

It should be noted that in a case where porous processing is performedto the reinforcing plate material, the inside material, the outsidematerial, and the like, a diameter d (mm) of the holes is preferably 0.7t≦d≦1.3 t with thickness of the plate material to which the porousprocessing is performed is t (mm). It should be noted that the thicknesst (mm) of the plate material is approximately 0.8 mm≦t≦1.2 mm. With thehole diameter in this range, for example perforation of punchingprocessing can be easily performed, so that mass-productivity isimproved.

Although the embodiments of the present invention are described above,the present invention is not limited to the above embodiments but can bevariously changed and implemented according to the description of theclaims. The present application is based on the Japanese patentapplication (Japanese Patent Application No. 2012-194106) filed on Sep.4, 2012, and contents thereof are taken herein as a reference.

EXPLANATION OF REFERENCE NUMERALS

-   1: Hood-   2: Outer material (outside material)-   3: Inner material (inside material)-   4: Reinforcing plate material-   5: Hole (through hole)-   S: Hollow portion

1. A porous sound absorbing structure, comprising: an outside materialhaving a smooth curved shape; an inside material having an uneven shapewith a perimeter thereof combined with a perimeter of the outsidematerial to form a hollow portion between the outside material and theinside material; and a reinforcing plate material having a plurality ofthrough holes, the reinforcing plate material being attached to an innersurface of at least any of the outside material and the inside materialon the side of the hollow portion in such a manner that an air layer isformed between the reinforcing plate material and the inner surface,wherein a sound absorbing property is given to an interior of the hollowportion by the reinforcing plate material, and the reinforcing platematerial being attached to and entirely positioned on an area of the atleast any of the outside material and the inside material, and thereinforcing plate material being positioned closer to a first end of thehollow portion than to a second, opposite end of the hollow portion. 2.The porous sound absorbing structure of claim 1, wherein an openingportion for guiding sound waves to the reinforcing plate material in thehollow portion is provided in at least any of the outside material andthe inside material.
 3. The porous sound absorbing structure accordingto claim 2, wherein the opening portion is provided at a position toface the reinforcing plate material.
 4. The porous sound absorbingstructure according to claim 1, wherein a plurality of through holes areformed in at least any of the outside material and the inside materialso that the sound absorbing property is given to at least any of theoutside material and the inside material.
 5. The porous sound absorbingstructure according to claim 1, wherein plate thickness t₁ (mm) of thereinforcing plate material is 0.8≦t₁≦1.2, and a diameter d₁ (mm) of thethrough holes provided in the reinforcing plate material is 0.7t₁≦d₁≦1.3 t₁
 6. The porous sound absorbing structure according to claim2, wherein the reinforcing plate material is attached to the innersurface of the outside material on the side of the hollow portion andthe opening portion is provided in the inside material.
 7. The poroussound absorbing structure according to claim 6, wherein a plurality ofopening portions are provided in the inside material, each of theopening portions is facing the reinforcing plate material.
 8. The poroussound absorbing structure according to claim 7, wherein the reinforcingplate material is formed in a substantially oblong shape in a plan viewand a sound absorbing portion with a large number of through holes isformed in the inside material where the position of the sound absorbingportion is set on the inside material closer to the second, opposite endof the hollow portion than to the first end such that the soundabsorbing portion is displaced from the reinforcing plate material. 9.The porous sound absorbing structure according to claim 1, wherein asectional shape of the reinforcing plate material is such that thereinforcing plate material has two mountain portions and a valleyportion in between such that the air layer is formed between a contourof the inner surface of the reinforcing plate material and the innersurface of the at least any of the outside material and the insidematerial.
 10. The porous sound absorbing structure according to claim 4,wherein a sound absorbing portion with a large number of through holesis formed in the inside material where the position of the soundabsorbing portion is set on the inside material such that the soundabsorbing portion is displaced from the reinforcing plate material. 11.The porous sound absorbing structure according to claim 1, wherein noopening portions are provided in the inside material and in the outsidematerial.
 12. The porous sound absorbing structure according to claim 1,wherein the reinforcing plate material has a plurality of mountingportions and at least one valley portion in a cross sectional view ofthe reinforcing plate material, such that the air layer is formedbetween the inner surface and the contour of the mounting portions andthe valley portions such that the thickness of the air layer is notuniform at all locations of the reinforcing plate material.
 13. Theporous sound absorbing structure according to claim 1, wherein a glassis partially housed in the hollow portion and the reinforcing platematerial is positioned between the glass and the at least any of theoutside material and the inside material.
 14. The porous sound absorbingstructure according to claim 1, wherein the reinforcing plate materialis a first reinforcing plate material that is attached to the outsidematerial and a second reinforcing plate material having a plurality ofthrough holes is attached to the inside material.
 15. The porous soundabsorbing structure according to claim 14, wherein the secondreinforcing plate material is attached to and positioned entirely on anarea of the inside material closer to the first end of the hollowportion than to the second, opposite end of the hollow portion.
 16. Theporous sound absorbing structure according to claim 15, wherein a glassis positioned in the hollow portion and at least a portion of the glassis positioned between the outside material and the inside material.